Generally, in a production step of a semiconductor device, a fine pattern is formed using a photolithographic method. Further, in forming the fine pattern, a large number of substrates called photomasks are usually used. In a photomask, a light-shielding fine pattern of a metal thin film or the like is generally provided on a transparent glass substrate. The photolithographic method is also used in manufacturing this photomask.
The photomask and the imprinting mold (namely, imprinting mold) serve as an original plate for transferring the same fine pattern to a great number of objects. The dimensional accuracy of a pattern formed on the photomask directly affects the dimensional accuracy of the fine pattern to be manufactured. Further, the imprinting mold is adapted to transfer a pattern by pressing the imprinting mold directly against a resist film applied on a transfer object, and thus, the shape in section of the pattern further seriously influences the shape of the fine pattern to be manufactured. With an increase in degree of integration of a semiconductor circuit, the dimensions of the pattern become smaller, and a higher accuracy or precision of the photomask or the imprinting mold is required. In particular, the imprinting mold adopts a transfer method by pressing the mold directly against the object as described above and the pattern is transferred at the same size, and thus, the required accuracy should be the same as the accuracy of the semiconductor circuit pattern. Therefore, the imprinting mold should be manufactured more accurately than a photomask.
In manufacturing a conventional imprinting mold, a mask blank is used which comprises a transparent substrate such as quartz glass and a thin film of chromium or the like formed thereon. After a resist is applied on the mask blank, a resist pattern is formed by using electron beam exposure or the like. By etching the thin film by using the resist pattern as the mask, a thin film pattern (mask pattern) is formed.
Further, with regard to an imprinting mold used for a transfer object on which a photo-curable resin is applied, for the purpose of applying light in transfer, a transparent substrate is etched with a thin film pattern used as the mask to manufacture a step pattern. In this case also, the dimensions and the accuracy of the pattern of the transparent substrate are directly affected by the dimensions and the accuracy of the thin film pattern. Therefore, in order to finally manufacture an imprinting mold having a highly accurate fine pattern formed thereon, it is necessary to form the thin film pattern in the mask blank with high pattern accuracy.
For example, as means for etching a thin film containing chromium or the like, wet etching using di-ammonium cerium(IV) nitrate or dry etching using a mixed gas of a chlorine-based gas and oxygen is ordinarily used.
Conventionally, there are known a method in which a thin film pattern including a plurality of layers is formed using multistage etching for the purpose of improving nonuniformity in width and depth of etching of a chromium film (Patent Document 1), and another method in which a thin film pattern is formed by using a resist pattern as the mask and, then, the thin film pattern thus formed is used as a mask to form a next thin film pattern of second and subsequent layers, in order to make it possible to thin a resist (Patent Document 2).
In the meanwhile, in a magnetic disk to be mounted to a magnetic recording device such as a hard disk drive (HDD), use has conventionally been made of a technique in which a higher density is sought by minimizing the width of a magnetic head and narrowing a space between data tracks in which information is recorded. However, the conventional technique has reached the limit in achieving a higher density, and magnetic effect between adjacent tracks and thermal fluctuation phenomena are no longer negligible. In recent years, a proposal has been offered about a new type of medium called Discrete Track Recording Medium (hereinafter referred to as a DTR medium) in which data tracks of a magnetic disk are formed so as to be magnetically separated.
The above-mentioned DTR medium seeks to improve the signal quality by removing a portion of a magnetic material which is unnecessary for recording (forming a groove). Further, after forming a groove, the groove is filled with a non-magnetic material to realize surface flatness at the angstrom level which is required for a magnetic disk drive. As one of techniques of forming the groove having a fine width, an imprinting technology is used.
Further, proposal has also been made of another new type of medium called a patterned medium (a medium in which a signal is recorded as a dot pattern), which is an advanced type of DTR medium with a further higher density. In forming a pattern for the patterned medium, also, the imprinting technology is promising.